The present invention relates to automatic electric circuit breakers, and particularly to circuit breakers having high fault current interrupting capacities.
Manufacturers of automatic electric circuit breakers are increasingly being faced with the task of developing new circuit breaker designs and upgrading existing circuit breaker designs to achieve higher current interrupting capacities in order to cope with the ever increasing current availables posed by modern applications. That is, due to the updating of electrical utility equipment, the magnitude of current available to feed a circuit fault has increased significantly, and it becomes the task of the circuit breaker protecting the faulted circuit to safely interrupt this higher fault current. Thus, the interrupting capacity of a circuit breaker has become a most critical performance parameter.
The most direct approach to achieving increased interrupting capacity is to provide a fast acting circuit breaker. That is, a circuit breaker will have an easier interrupting task if it is capable of effecting contact separation early in a fault current wavefront and thereby begin developing an arc voltage in opposition to the fault current driving voltage before the fault current achieves its prospective peak. This is due to the fact that such early development of an arc voltage is effective in cresting the fault current at actual peak amplitude which is less than its prospective peak amplitude. Equally important is the circuit breaker's ability to not only sustain this arc voltage, i.e., prevent contact reclosure, but to rapidly increase the arc voltage to a level in excess of the driving voltage so as to drive the fault current to a premature zero. Typically, the requisite rapid rise in the arc voltage is jointly achieved by rapidly increasing contact separation and by providing requisite arc handling means in the form of arc runners and arc chutes to further lengthen the arc, chop the arc into a series of arclets, and cool the arc. If the arc handling means achieves an arc quench while retaining sufficient dielectric strength to prevent restrike, a successful interruption is effected.
It is accordingly an object of the present invention to provide an automatic electric circuit breaker having increased interrupting capacity.
A further object is to provide an exceptionally fast acting circuit breaker of the above character.
Another object is to provide a circuit breaker of the above character wherein early contact separation is achieved automatically in response to a fault current.
Yet another object is to provide a circuit breaker of the above character wherein early contact separation is achieved independently of and unencumbered by the circuit breaker contact operating mechanism.
A still further object is to provide a circuit breaker of the above character wherein contact separation is motivated by the electrodynamic forces associated with the fault current.
Another object is to provide a circuit breaker of the above character having improved arc handling capabilities.
Still another object of the present invention is to provide a circuit breaker of the above character which is efficient in construction and reliable in operation.
Other objects of the invention will in part be obvious and in part appear hereinafter.